It is a common practice in pressure-sensitive adhesive applications to use additive resins to modify the adhesive properties, and patent literature abounds in the same. Most of the prior art teaches the use of resins such as rosin esters, terpene phenolic resins, hydrocarbon resins, and the like, to improve certain properties of the pressure-sensitive adhesive, such as peel adhesion. The improvement in peel adhesion is normally achieved at the expense of high temperature shear holding power and/or high shear adhesion failure temperature (SAFT). Most of the resins are nonreactive with the polymer and have a tendency to migrate on long term aging or degrade unless anti-oxidants are added, antioxidants also have a tendency to alter the properties originally intended for the pressure-sensitive adhesive composition.
Japanese Patent Publication 8418774 (Hitachi Chemical Co.) discloses the use of radiation curable tackifiers in acrylic pressure-sensitive to provide high initial adhesive and cohesive strengths. The patent teaches the use of glycidyl methacrylate modified rosin acids and terpene phenolic resins which can be made to cross-link by irradiating with electron beam radiation. No mention was made of the shear performance at elevated temperatures. The modification reaction is different from the subject of this invention.
U.S. Pat. No. 4,380,513 to Ruckel et al. deals with the preparation of inert rosin esters by reacting lower aliphatic saturated carboxylic acids, anhydrides and acid chlorides with the hydroxide groups of the rosin ester. The product of the reaction is inert in that it does not carry any copolymerizable reactive functionality.
U.S. Pat. No. 4,377,513 to Ruckel et al. discloses the use of a urethane modified rosin ester of primary polyhydric alcohol as a tackifier for polar elastomer adhesives such as polyurethanes. According to the patentees, a polyhydric alcohol was esterified (50-95% with rosin acid and the remaining hydroxy groups reacted with phenyl isocyanate or toluene di-isocyanate. The tackifier does not have vinyl functionality and is not intended for use with pressure-sensitive adhesives.
U.S. Pat. No. 4,418,120 to Kealy et al. discloses tackified, chemically cross-linked acrylic pressure-sensitive adhesives. The polymer used in the adhesive has very high precure molecular weight with an inherent viscosity of 0.75-1.5 dl/g to accommodate high levels of tackifying rosin esters. The formulated adhesive contains select antioxidants to prevent the aging of the tackifier. The tackifiers used are again nonfunctional.
U.S. Pat. No. 4,726,982 to Traynor et al. teaches N-vinyl-2-pyrrolidone containing acrylic pressure-sensitive adhesives, which when mixed with tackifying resins such as rosin esters, alkylated styrenes, and the like, and on UV curing, give improved adhesion to high solids automotive paint systems. The resins do not have vinyl functional groups as revealed in the present invention and high amounts of (&gt;10%) N-vinyl pyrrolidone is copolymerized to achieve the desired properties.